Ground proximity warning system

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Ground proximity warning system (GPWS) is a system designed in 1967 by Don Bateman Chief Engineer of Flight Safety Avionics at AlliedSignal now Honeywell[citation needed], to alert pilots if their aircraft is in immediate danger of flying into the ground or an obstacle. Another common name for such a system is ground-collision warning system (GCWS).

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[edit] Commercial aircraft

The system monitors an aircraft's height above ground as determined by a radar altimeter. A computer then keeps track of these readings, calculates trends, and will warn the captain with visual and audio messages if the aircraft is in certain defined flying configurations ("modes").

The modes are:

  1. Excessive descent rate ("PULL UP" "SINKRATE")
  2. Excessive terrain closure rate ("TERRAIN" "PULL UP")
  3. Altitude loss after take off ("DON'T SINK")
  4. Unsafe terrain clearance ("TOO LOW - TERRAIN" "TOO LOW - GEAR" "TOO LOW - FLAPS")
  5. Excessive deviation below glideslope ("GLIDESLOPE")
  6. Bank angle protection ("BANK ANGLE")
  7. Windshear protection ("WINDSHEAR")

Don Bateman, a Canadian born engineer, is credited with the invention of GPWS.[2] He spearheaded the development of GPWS in the late 1960s after a series of controlled flight into terrain (CFIT) accidents killed hundreds of people.

Prior to the development of GPWS, large passenger aircraft were involved in 3.5 fatal CFIT accidents per year, falling to 2 per year in the mid-1970s. Since 1974, when the U.S. Federal Aviation Administration made it a requirement for large aircraft to carry such equipment, there has not been a single passenger fatality in a CFIT crash by a large jet in U.S. airspace.[3] In 2000 the FAA extended the requirement to smaller commuter aircraft.

Traditional GPWS does have a blind spot. Since it can only gather data from directly below the aircraft, it must predict future terrain features. If there is a dramatic change in terrain, such as a steep slope, GPWS will not detect the aircraft closure rate until it is too late for evasive action.

In the late 1990s improvements were made and the system was renamed "Enhanced Ground Proximity Warning System" (EGPWS/TAWS). The system was now combined with a worldwide digital terrain database and relies on Global Positioning System (GPS) technology. On-board computers compared its current location with a database of the Earth's terrain. The Terrain Display now gave pilots a visual orientation to high and low points nearby the aircraft.

EGPWS software improvements were focused on solving two common problems; no warning at all, and late or improper response.

No Warning: The primary cause of CFIT occurrences with no GPWS warning is landing short. When the landing gear is down and landing flaps are deployed, the GPWS expects the airplane to land and therefore, issues no warning. EGPWS introduces the Terrain Clearance Floor (TCF) function, which provides GPWS protection even in the landing configuration.

Late Warning or Improper Response: The occurrence of a GPWS alert typically happens at a time of high workload and nearly always surprises the flight crew. Almost certainly, the aircraft is not where the pilot thinks it should be, and the response to a GPWS warning can be late in these circumstances. Warning time can also be short if the aircraft is flying into steep terrain since the downward looking radio altimeter is the primary sensor used for the warning calculation. The EGPWS improves terrain awareness and warning times by introducing the Terrain Display and the Terrain Data Base Look Ahead protection.

In Commercial and Airline operations there are legally mandated procedures that must be followed should an EGPWS caution or warning occur. Both Pilots must respond and act accordingly once the alert has been issued. An Indonesian Captain has been charged with manslaughter for not adhering to these procedures [1].

[edit] General Aviation

The EGPWS equipment is not a legal requirement in piston engined aircraft. Depending on the type of operation, EGPWS is only required to be installed into Turbine powered aircraft with 10 or more passenger seats [2].

A smaller and less expensive version of EGPWS was developed by AlliedSignal (now merged with Honeywell) for General Aviation and Private Aircraft [3].

[edit] Military fast jet

For military fast-jets, the high speed and low altitude which may frequently be flown, make traditional GPWS systems unsuitable as the “blind spot” becomes the critical part. Thus an enhanced system is required, taking inputs not only from RadAlt but also from LINS, GPS, and FCS, and using these to accurately predict the flight path of the aircraft up to four or five miles ahead. Digital maps of terrain and obstacle features are then used to determine whether a collision is likely if the aircraft does not pull up at a given pre-set g-level. If a collision is predicted a cockpit warning may be provided. This is the type of system deployed on such aircraft as Eurofighter Typhoon. [4]

[edit] See also

[edit] External links


[edit] References

  1. ^ ATW: Yogyakarta crash captain arrested, charged with manslaughter
  2. ^ FAA Part135 [1]
  3. ^ AeroWorldNet(tm) - AlliedSignal Develops New EGPWS, Display for General Aviation Market [May 17, 1999]
  4. ^ Eurofighter Typhoon - BAE SYSTEMS delivers first Eurofighter Typhoon Ground Proximity Warning
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